C++ Interfaces and Abstract Classes

In the realm of C++, an interface shines as a vibrant description of a class’s behavior and capabilities, al

l without being shackled to a specific implementation. This flexibility sets the stage for the powerful concept of abstract classes, a cornerstone of C++’s prowess.

C++ interfaces come to life through the medium of abstract classes, a concept distinct from data abstraction. The latter conceals implementation intricacies from associated data, while abstract classes provide a blueprint for inheritable behavior. In C++ interfaces and abstract classes play a crucial role in achieving abstraction and defining a contract for derived classes to implement.

To transform a class into an abstract class, at least one of its functions must be declared as a pure virtual function. This involves appending “= 0” to the function’s declaration. For instance:

class Box {
   public:
      // Pure virtual function
      virtual double getVolume() = 0;

   private:
      double length;      // Length of a box
      double breadth;     // Breadth of a box
      double height;      // Height of a box
};

Abstract classes are designed to serve as the basis for inheritance. They cannot be instantiated directly, instead, they exist to provide a well-structured inheritance foundation. Attempts to instantiate an abstract class lead to compilation errors.

For a subclass of an abstract base class to be instantiated, it must implement all the virtual functions. This compels adherence to the interface declared by the abstract base class. Neglecting to override a pure virtual function in a derived class, followed by attempts to instantiate that class, triggers a compilation error.

Concrete classes, those capable of object instantiation, spring forth from this design.

Abstract Class in Action: An Illustration

Let’s delve into an illustrative C++ example:

#include <iostream>

using namespace std;

// Base class
class Shape {
   public:
      // Pure virtual function providing an interface framework.
      virtual int getArea() = 0;
      void setWidth(int w) {
         width = w;
      }

      void setHeight(int h) {
         height = h;
      }

   protected:
      int width;
      int height;
};

// Derived classes
class Rectangle: public Shape {
   public:
      int getArea() { 
         return (width * height); 
      }
};

class Triangle: public Shape {
   public:
      int getArea() { 
         return (width * height)/2; 
      }
};

int main(void) {
   Rectangle Rect;
   Triangle  Tri;

   Rect.setWidth(5);
   Rect.setHeight(7);

   // Print the area of the object.
   cout << "Total Rectangle area: " << Rect.getArea() << endl;

   Tri.setWidth(5);
   Tri.setHeight(7);

   // Print the area of the object.
   cout << "Total Triangle area: " << Tri.getArea() << endl; 

   return 0;
}

In this code, the abstract class Shape unveils the pure virtual function getArea(). The Rectangle and Triangle classes then inherit from Shape, manifesting the essence of abstraction. While both classes implement the same function, they employ distinct algorithms tailored to their shapes.

Architecting for Resilience with Abstract Classes

The abstract class shines as a beacon of resilient design, propelling flexible and extensible solutions. Through adherence to the interface outlined by the abstract class, derived classes harmonize with its blueprint.

In the symphony of object-oriented programming, abstract classes conduct the orchestra. They provide a harmonious platform for diverse applications, each translating the standard interfaces into concrete, functional behavior.

This architectural elegance ensures that new applications can seamlessly integrate into the system, even after its initial design. The abstract class preserves the essence of interface-centric development while laying the foundation for boundless extensibility.